1. Field of the Invention
The present invention relates to an ink jet printing apparatus that carries out printing using ink.
2. Description of the Related Art
Printing apparatuses have functions for a printer, a copier, or a facsimile machine or are used as output equipment for composite electronic equipment or a workstation including a computer or a word processor. These printing apparatuses are configured to print images on printed materials (print media) such as paper or thin plastic sheets on the basis of image information. The printing apparatuses can be classified into an ink jet type, a wire dot type, a thermal type, a laser beam type, and others in terms of a printing method.
A serial type printing apparatus employs a serial scan method of moving the apparatus in a main scanning direction crossing a direction (sub-scanning direction) in which printed materials are conveyed. In this printing apparatus, printing means mounted on a carriage moving along the main scanning direction is used to print an image (main scanning). After one row has been printed, the printed material is conveyed a predetermined amount (pitch feed). Subsequently, the printed material is stopped again, and the next row of the image is printed (main scanning). These operations are alternately repeated to print the entire printed material.
On the other hand, a line type printing apparatus carried out printing simply by conveying a printed material (sub-scanning) and without moving the print head. In this printing apparatus, a printed material is set at a predetermined print position. One row is printed at a time, and then the printed material is conveyed a predetermined amount (pitch feed). Then, the next row is printed at a time. These operations are repeated to print the entire printed material.
Of the above printing apparatuses, a printing apparatus based on the ink jet method (ink jet printing apparatus) carries out printing by allowing printing means (the print head) to eject ink to a printed material for printing. The ink jet printing apparatus has a large number of advantages. For example, its printing means can be made smaller easily, and it can print an image with a high resolution at a high speed. Furthermore, the ink jet printing apparatus requires less running costs and involves less noise because of the use of a non-impact method. Moreover, the ink jet printing apparatus can easily print color images using a large number of color inks. In particular, printing operations can be performed at a higher speed using a line type printing apparatus that uses line type printing means having a large number of ejection openings arranged in the cross direction (main scanning direction) of printed media.
However, if a printing operation is performed using the ink jet method, then in addition to ink droplets contributing to image printing, fine ink droplets (ink mists) not contributing to image printing are ejected from the print head. The ink mists have small shapes and light weights and may flow in the air and adhere to various sites inside the apparatus in the form of stains. Furthermore, the ink mists adhering to a platen or a print sheet conveying guide member also adhere to print media in the form of stains. They may hinder the formation of appropriate print images. However, when the ink mists adhering to and accumulating on the platen, a print paper conveying roller, or the like become more viscous, the print medium cannot be smoothly conveyed. The print sheets maybe jammed or inappropriately conveyed, for example, they may be conveyed obliquely, wrinkled, or waved. Moreover, if ink mists adhere to the vicinity of a movable part such as a sliding shaft or bearing on a carriage, the movable part may undergo severer friction to disable normal operations.
Furthermore, if ink mists adhere to an encoder located near the carriage or an optical part such as a reflection type photo sensor used to detect the position of a print medium or the carriage, it becomes impossible to accurately monitor the position or speed of the carriage or print medium. Consequently, the apparatus cannot be operated correctly. If ink mists adhere to an electric part, the ink may cause a short circuit, corrosion of a structural part, or even damage to the printing apparatus, depending on the composition of the ink. Further troubles may occur. For example, the ink mists may fly out of the printing apparatus through an opening and adhere to and accumulate on a part such as a cover of the printing apparatus which may be touched by an operator or a work surface around the printing apparatus. Consequently, the periphery of the apparatus may be contaminated with the ink, or the operator may be stained with ink when scanning the printing apparatus.
To eliminate these disadvantages, an arrangement has been proposed in which a fan and a duct are provided near a printing section including the print head, the carriage, and the platen in order to generate air currents (refer to Japanese Patent Application Laid-Open Nos. 6-126952 (1994), 6-166173 (1994), and 7-025007 (1995)).
In connection with the ink jet printing apparatuses described in the above patent documents, a printer is proposed which is provided with a fan in order to facilitate the fixation of ink landing on a print medium and remove ink mists. The fan is controlled to operate only during printing operations.
However, with the conventional ink jet printing apparatus provided with the fan as described above, the driving of the fan is stopped simultaneously with the end of a printing operation or with the stoppage of the carriage. Alternatively, the fan is always driven. A problem with the former method is that the driving of the fan is stopped simultaneously with the stoppage of a printing operation even though ink mists floating in the printing apparatus have not been completely removed. A problem with the latter method is that the fan is driven even though ink mists have been completely removed, resulting in wasteful power consumption.